1. Field of the Invention
The present invention concerns carbodiimide-modified organic polyisocyanates. More particularly, the present invention relates to a process for preparing liquid carbodiimide-modified polyisocyanates employing organotin catalysts.
2. Prior Art
The prior art discloses a number of patents for the conversion of polyisocyanates containing carbodiimide groups employing various catalysts, among which, as disclosed in U.S. Pat. No. 4,085,140, is a co-catalyst system of cyclic phosphorus compounds and a tertiary amine. Another U.S. Pat. No. 3,640,966 discloses the preparation of polyisocyanates containing carbodiimides by employing catalytic amounts of a catalyst which is an organic isocyanate compound containing biuret, urea, amido, isocyanurate, uretedione, or uretonimine groups in the compound.
Still another patent, U.S. Pat. No. 3,670,502, claims a process for the preparation of carbodiimide-containing organic polyisocyanate by employing catalytic amounts of tris(chloromethyl)phosphine oxide. U.S. Pat. No. 3,449,256 claims the preparation of carbodiimide-modified polyisocyanates by heating the polyisocyanate with trihydrocarbyl phosphate.
U.S. Pat. No. 3,426,025 teaches a process for the preparation of organic carbodiimide-modified polyisocyanates by the use of a metallic derivative of an organic hydroxy compound which metal may be lithium, sodium, potassium, boron, titanium, hafnium, zirconium, niobium and silicon. U.S. Pat. No. 3,396,167 claims and teaches the preparation of isocyanurates by condensing a monoisocyanate in the presence of an organotin compound. None of the prior art teaches, or even suggests, that carbodiimide-containing organic polyisocyanates may be prepared by employing organotin compounds as taught by the instant invention.